For example, as disclosed in each of Japanese Patent Application Laid-Open No. H1-315914 (Patent Document 1) and Japanese Patent Application Laid-Open No. H11-317134 (Patent Document 2), a vacuum valve is formed of an insulating material such as a glass material or a ceramic material and includes a cylindrical, bottomed vacuum container whose inside gas is exhausted so as to be high-vacuum, respective electrode rods provided at both ends of the vacuum container, spiral-ring-shaped coil electrodes provided at the respective electrode-rod tips that face each other, and respective disk-shaped contacts connected with the coil electrodes; one of the electrode rods is moved in the axis direction, so that the both contacts (i.e., the fixed-side contact and the movable-side contact) are made to make contact with or separate from each other and hence energization or cutoff is performed.
The coil electrode is explained in each of Patent Documents 1 and 2; i.e., on the rear side of each of the both contacts, a plurality of circular-arc-shaped coil sections are separately arranged in the circumferential direction along the outer circumferential edge of the contact so that an axis-direction magnetic field is produced in the contact/separation direction of the fixed-side and movable-side contacts as the main electrodes; one end of the coil section has an arm section extending toward the center and the other end thereof has a protruding section to be connected with the contact.
In the foregoing vacuum valve, the coil electrode generates an axis-direction magnetic field at a time of energization, and an inter-contact electric arc inevitably produced at a time of cutoff is confined within the diameter of the contact and is concurrently dispersed on the surface of the contact so that the current density on the contact surface is lowered; thus, the cutoff capability of the contact material becomes superior and hence the current can be cut off.
In order to enlarge the cutoff capacity of the vacuum valve, it is indispensable to develop the coil electrode and the contact material; thus, to date, various studies have been carried out. As a result, it is known that the cutoff performance of a vacuum valve is raised in proportion to the intensity, the uniformity, and the area of the axis-direction magnetic field generated by a coil electrode.